Many industries use aqueous compositions for the surface treatment of metals, ceramics, glasses, and plastics. Cleaning, plating, and deposition of coatings are often carried out in aqueous media and are usually followed by a step in which residual water is removed. Hot air drying, centrifugal drying, and solvent-based water displacement are common methods used to remove such residual water.
For many years, 1,1,2-trichlorotrifluoroethane (CFC-1 13) has been the preferred solvent in cleaning and drying or dewatering applications. Recently, chiorofluorocarbons (CFCs) such as CFC-113 have come under regulation as they are believed to contribute to depletion of the earth's stratospheric ozone layer. These regulations have reduced and phased-out the production of CFCs and thereby their release into the earth's atmosphere. Thus, there is a continuing industry need for alternatives to CFC-based compositions.
Hydrofluorocarbons (BFCs) have been proposed as replacements for CFCs in cleaning and drying compositions. Illustrative of such HFC compositions are those described in U.S. Pat. Nos. 5,578,137, 5,514,301, and 5,610,128. Many HFCs have limited solvency for water and hydrocarbon oils and soldering flux residues. The use of surfactant which assists in removal of such materials from substrates is therefore necessary in many drying and cleaning applications of HFCs. Halocarbon solvents containing a hydrophobic surfactant have been used to displace water from substrates. However, identification of an appropriate solvent/surfactant pair to accomplish water displacement and residue cleaning is not trivial.
Many HFCs are unable to dissolve conventional surfactants designed for use with chlorocarbon, chlorofluorocarbon, and hydrochlorofluorocarbon solvents. Not only must surfactants which are soluble in a given HFC be identified, but also those having the desired properties and activity for a given application. It has been a problem in this field to find hydrophobic surfactants that are essentially insoluble in water, will not form an emulsion with water, and yet are still able to displace water or clean process residue from a variety of substrates.
Conventional displacement drying fluids such as Freon.RTM. T-DA and Freon.RTM. T-DFC marketed by E. I. duPont de Nemours & Co., Wilmington, Del., USA (DuPont), contain low concentrations of highly effective alkyl phosphate amine salt surfactants, such as a 1:1 salt of 2-ethylhexyl amine and isooctyl phosphate, that rapidly release water from surfaces by lowering surface tension. Unfortunately, conventional surfactants such as these are insoluble in HFC solvents.
There is a need in the displacement drying field to find soluble displacement drying surfactants for use in HFC solvents such as 1,1,1,2,2,3,4,5,5,5-decafluoropentane (CF.sub.3 CF.sub.2 CFHCFHCF.sub.3, HFC 43-10mee), which form effective drying compositions at surfactant concentrations of around 0.1 weight percent (wt %) in HFC, and which have very low water solubility.
Certain non-ionic surfactants such as ethoxylated alcohols, mercaptans, or alkylphenols are soluble in HFC 43-10mee. Such surfactants have drying efficiencies of only 50 to 70% of the conventional CFC-113-based drying compositions, require high surfactant concentration which results in substrate rinsing and staining problems, and are water soluble resulting in surfactant loss with the water discharge.
Surprisingly and unexpectedly, it has been discovered that the surfactants of the present invention enhance the performance of HICs such as HFC 43-10mee and other hydrochlorofluorocarbon and hydrofluorocarbon ether halocarbon solvents in displacement drying. The present invention includes a new class of hydrophobic, HFC soluble, fluorinated surfactants with surface activity in HFCs resulting in highly effective displacement drying compositions. More particularly, the present invention includes dewatering and cleaning compositions comprising a HFC solvent and an effective amount of an of a alkylammonium salt of a fluorinated phosphate ester.
Zyhowski et al. in U.S. Pat. No. 5,610,128 disclosed surfactants which are quaternary ammonium salts of alkyl phosphates for use in HFCs for drying and cleaning. Fluoroalkyl groups may be present on the ammonium and/or phosphate ions. The preferred structures have the fluoroalkyl group only on the ammonium ion.
Bil et al. in U.S. Pat. No. 5,514,301 disclosed dewetting or degreasing compositions based on halogenated aliphatic solvents containing in solution at least one mono- or dialkyl phosphate of a fluorinated amine, at least one quaternary ammonium mono- or dialkyl phosphate and optionally a quaternary ammonium chloride.